FAQ

Knowledge Base

FREQUENTLY ASKED QUESTIONS

Everything you need to know about biofilm, Hydro Dioxide, and how combined treatments deliver cleaner, safer water.

Biofilm is a slimy layer of microorganisms, including bacteria and algae, that attaches to pool surfaces, hidden plumbing, heating systems and other equipment. It forms when free-floating bacteria find a surface to cling to and secrete a protective, sticky organic matrix. Warm water, poor circulation and inadequate sanitation create the perfect breeding ground for this matrix to grow rapidly.

Biofilms act like a shield, making microorganisms much more resistant to chlorine and other disinfectants. Pathogens such as Pseudomonas aeruginosa and Legionella can survive inside biofilms even when water chemistry appears to be within acceptable limits.

Microbes released from biofilms can contaminate the pool water and potentially cause skin rashes and ear infections, respiratory and gastrointestinal illnesses, while also increasing maintenance requirements and costs.

Yes
Standard pool sanitisers, such as chlorine, struggle to penetrate the protective matrix of biofilms and effectively destroy the bacteria sheltered within. As a result, the pool system continually requires increasing amounts of chemicals in an attempt to break down this barrier and maintain safe, clean water. This leads to a continuous cycle of overdosing sanitisers and algaecides, higher Total Dissolved Solids, generally poorer water conditions and increasing operational costs while the underlying problem remains unresolved.
Biofilm can negatively impact pool surfaces by creating a persistent layer of organic material that traps microorganisms and contaminants against the surface. Over time, microbial activity can produce by-products that contribute to staining, discolouration and deterioration of pool finishes, including liners, tiles and plaster.

If left unmanaged, biofilm growth can increase surface degradation and may result in higher maintenance requirements, costly repairs or the premature replacement of affected materials.

All sorts of microorganisms can lay low in the safety of a biofilm. Two of the most dangerous to health include Pseudomonas aeruginosa and Legionella. The hardy oocysts of the parasite Cryptosporidium can become trapped in surface biofilms, evading detection and chlorine disinfection, only to be released into water supplies later, potentially causing cryptosporidiosis outbreaks.
Yes. The localised environment created beneath the biofilm layer traps corrosive by-products and moisture directly against metal surfaces. This aggressive process, known as Microbiologically Influenced Corrosion (MIC), attacks metallic pool equipment such as heat exchangers, ladders and pump components. Over time, this corrosion drastically reduces the lifespan of expensive pool hardware.
While both are effective disinfectants, they work in very different ways. Chlorine donors (hypochlorous acid) release free chlorine, which disinfects water but is quickly used up by organic matter and cannot effectively penetrate biofilms, where bacteria can hide. Hydro Dioxide (chlorine dioxide) works by oxidation rather than chlorination, allowing it to penetrate and break down biofilm while killing bacteria, viruses and other microorganisms. It also does not produce chloramines or trihalomethanes (THMs, chloroform or HAAs), the by-products associated with pungent chlorine odours and traditional chlorine treatment, helping to maintain cleaner, higher-quality water.
Chlorine is an effective disinfectant, but it is quickly used up as it reacts with dirt, organic matter and biofilm, reducing its effectiveness over time. By oxidising microorganisms rather than chlorinating them, Hydro Dioxide (chlorine dioxide) penetrates and breaks down biofilm, reaching bacteria and parasites that chlorine may miss.

Used alongside existing treatment processes, Hydro Dioxide provides more complete system disinfection and helps maintain cleaner, safer water throughout the entire system, keeping the plant, operators and bathers safe.

Safe and available in tablet form, Hydro Dioxide is manufactured in Scotland, UK, and is exclusively distributed by GreenTech International. It offers a preventative and proactive approach to biofilm control using stabilised chlorine dioxide technology. Unlike traditional chlorine biocides, Hydro Dioxide is specifically designed to penetrate biofilm layers and eliminate the microorganisms protected within them, reducing the risk of persistent contamination and recurring bacterial issues.

The product’s broader oxidative capability enables effective treatment against bacteria, fungi and resistant protozoans, including Cryptosporidium and Giardia, pathogens specifically referenced within HSG282 guidance relating to spa pool safety and Legionella control.

Unlike many chlorine dioxide products, Hydro Dioxide falls below 5.1 oxidiser classification and does not carry GHS06 or GHS08 hazard classifications.

The product also holds EN 1276 certification, demonstrating a log 5 reduction (99.999%) against selected microbes including Pseudomonas aeruginosa.

Hydro Dioxide is incredibly easy to administer. Effervescent tablets dissolve very quickly and can be applied directly to swimming pool water, balance tanks, filter media and drainage gulleys. Green Tech International is also in the process of designing an automated dosing system that can be added to existing pool plant to simplify the process even further. This is due to enter the market in 2027/28.
Hydro Dioxide is fully compliant with GB BPR PT 2 and our partners at Scotmas Group are certified under the following quality systems: ISO 9001 Quality Management, ISO 45011 (the new standard for OHSAS), ISO 14001 Environmental Management and ISO 13485 Medical Devices.
Chlorine dioxide (ClO₂) is widely recognised as highly effective at killing and dispersing biofilms. A dosage of 0.2 mg/L (ppm) is sufficient to penetrate biofilms. A regular monthly maintenance dose should be part of the proactive water management regime.

Green Tech International is working in partnership with Coventry University (Knowledge Transfer and PhD Students) facilitating research projects later this year for the efficacy of chlorine dioxide in recreational water against biofilms, improved water sustainability, Cryptosporidium and disinfection by-products.


Water Sustainability


Water is a precious resource, and the UK faces a massive crisis, with the Environment Agency predicting a water supply shortfall of up to 5 billion litres per day by the 2050s. Driven by climate change and population growth, demand could outstrip supply by mid-century unless radical steps are taken to curb consumption.

Therefore, the proactive intervention of Hydro Dioxide against biofilms and hard-to-treat microbes such as Pseudomonas aeruginosa and parasites including Cryptosporidium will help improve water consumption within the recreational water industry and meet the challenge we all face.

Standard tablets release free chlorine to maintain water safety, but they are quickly consumed when fighting hidden biofilm. By using Hydro Dioxide (ClO₂) to completely eradicate the biofilm matrix, your chlorine is no longer wasted on the plumbing walls. This means you will use significantly fewer tablets throughout the season while maintaining perfectly safe, crystal-clear water.
Liquid chlorine and salt electrolysis systems both provide excellent continuous sanitation, but they struggle against established slime. When you eliminate this organic burden with ClO₂, your automated dosing probes (ORP/Redox) will register clean water much faster. Consequently, your liquid chlorine pump will inject far less chemical, and your salt chlorinator cell can run at a much lower power setting, greatly extending its lifespan.
UV systems are highly effective at neutralizing free-floating pathogens as they pass through the light chamber. However, UV light provides no residual protection in the water and cannot reach the biofilm growing inside dark pipes or filter media. Adding Hydro Dioxide perfectly complements UV by deeply cleaning the entire plumbing network that the light simply cannot reach.
Hydrogen peroxide and potassium monopersulfate (KMPS) are fantastic for burning off organic waste and keeping water sparkling, but they cannot penetrate biofilm. By letting Hydro Dioxide handle the tough job of destroying the biofilm shield, these alternative oxidizers can focus entirely on clarifying the water. This combination ensures a gentle, odorless swimming environment with absolute microbiological safety.
Biofilm acts as a massive sponge that constantly consumes your standard sanitizers. Eradicating it drastically lowers your daily chemical consumption and saves you money. Furthermore, clean pipes have a wider internal diameter and lack sticky friction, allowing your filtration pump to push water more easily. This improved hydraulic efficiency leads to noticeably lower electricity bills over the swimming season.
Microorganisms living inside biofilm produce localized acidic waste that slowly eats away at pool liners, tiles, and plaster. They also trigger microbiologically influenced corrosion on expensive metal components like heat exchangers, sensors, and ladders. By proactively removing the biofilm with Hydro Dioxide, you stop this hidden degradation, preserving your pool's aesthetic appearance and delaying costly equipment replacements.
If you are using Hydro Dioxide for the first time, you should start with an initial deep-cleaning treatment. This curative dose is designed to completely strip away any mature biofilm that has already accumulated inside your hidden plumbing and filter media. Performing this purge at the beginning of the pool season sets a perfectly clean foundation for your primary sanitizers.

Once your system is clear, you can switch to a simple preventative maintenance schedule to keep the biofilm from ever returning. Adding a smaller dose of Hydro Dioxide every four to six weeks is generally enough to stop new organic matrices from taking root. This routine ensures your standard chlorine, salt, or UV systems continue to work at peak efficiency without wasting energy fighting hidden bacteria.

Additionally, applying a final dose right before winterizing your pool is highly beneficial. It guarantees your pipes remain completely sterile during the off-season, preventing nasty surprises and cloudy water when you reopen the pool in the spring.
Unlike traditional sanitizers, Hydro Dioxide (ClO₂) generates in situ a dissolved gas (ClO₂) that does not react with harmless organic matter in the water. This unique chemical selectivity allows it to easily penetrate the thick, sticky shield of the biofilm without losing its strength. Once inside, it actively destroys the cellular walls of hidden pathogens, including dangerous Legionella pneumophila and common water bacteria like E. coli or Pseudomonas.
Chlorine tablets rely on free active chlorine, which struggles to pierce the biofilm matrix and ends up just bleaching the surface layer. Additionally, tablets add cyanuric acid (stabilizer) to your water, which can quickly build up and block the chlorine's sanitizing power. Hydro Dioxide completely eliminates the biofilm from the roots and operates entirely without adding any cyanuric acid to your pool.
Saltwater electrolysis is a very convenient way to generate free active chlorine, but it produces the exact same chemical as traditional liquid chlorine. Therefore, it faces the same limitations: it cannot deeply penetrate established biofilm to kill the bacteria hiding inside. Hydro Dioxide works entirely differently as an oxidizing gas, actively stripping away the biofilm layer that salt-generated chlorine leaves behind.
Liquid bleach is a very convenient way to inject free active chlorine quickly with high concentration (0.15g/ml), but its active chlorine concentration within the barrel drops very fast (6 month lifetime). Therefore, it faces the same limitations as chlorine tablets: it cannot deeply penetrate established biofilm to kill the bacteria hiding inside. Hydro Dioxide works entirely differently as an oxidizing gas, actively stripping away the biofilm layer that salt-generated chlorine leaves behind — with a very long lifetime in its sachet.
Active chlorine highly depends on your pool's pH level to be effective and reacts with sweat and oils to form chloramines, which cause red eyes and strong chemical smells. Hydro Dioxide is completely effective across a very wide pH range (from 4 to 10) and does not form any irritating chloramines. It cleans your pipes and surfaces while keeping the water perfectly comfortable for swimmers.
Bromine is often used in warm water like spas because it remains more stable than chlorine at high temperatures. However, bromine is still a halogen sanitizer that lacks the specific chemical action needed to dismantle the tough, protective matrix of a mature biofilm. Hydro Dioxide provides superior stability in warm water while actively eradicating the biofilm structure that bromine cannot break down.
Hydrogen peroxide is an oxygen-based treatment that is gentle on the skin, but it is a relatively weak sanitizer at standard pool concentrations. It breaks down very quickly in the water and is completely ineffective at penetrating and destroying a biofilm colony. Hydro Dioxide offers the same gentle swimming experience but packs the necessary oxidizing power to eliminate severe bacterial contamination and Legionella.
Potassium monopersulfate (KMPS) is an excellent non-chlorine shock used to burn off organic waste and clear cloudy water. However, MPS is solely an oxidizer, not a standalone EPA-registered sanitizer, meaning it cannot kill bacteria or Legionella on its own. Hydro Dioxide acts as both a powerful oxidizer and a lethal sanitizer, making it a complete solution for deep cleaning hidden plumbing lines.

Treatment Comparison at a Glance

Treatment Method Biofilm Penetration Pathogen Efficacy (e.g. Legionella) Byproducts / Comfort pH Dependency Corrosive Impact Impact on Pool pH
Hydro Dioxide (ClO₂) Excellent (Destroys matrix) Extremely High (Kills within biofilm) None (No chloramines) Very Low (Works pH 4–10) Low (When dosed correctly) Neutral (Does not change pH)
Chlorine Tablets Poor (Surface bleaching only) Low (Cannot reach hidden bacteria) Adds cyanuric acid, forms chloramines & THM High (Requires strict pH 7.0–7.4) Moderate (High acidity near tablet) Lowers pH (Highly acidic)
Saltwater Electrolysis Poor Low (Cannot reach hidden bacteria) Forms chloramines & THM, raises pH High (Requires strict pH 7.0–7.4) High (Salt buildup on metals/stone) Constantly raises pH
Liquid Bleach Poor Low (Cannot reach hidden bacteria) Forms chloramines & THM, adds salt High (Requires strict pH 7.0–7.4) Moderate Constantly raises pH
Bromine Fair Moderate Bromamines (Less odor, but present) Moderate Moderate Slightly lowers pH
Hydrogen Peroxide Very Poor Very Low None Low High (At concentrated doses) Neutral
Monopersulfate (MPS) Poor None (Not a sanitizer) None Low Moderate Slightly lowers pH
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